Hydraulic Rotary Machine

ABSTRACT

A sliding layer ( 21 ) of a sintered copper alloy is formed on a sliding surface ( 12 A) of a valve plate ( 12 ). That is, the valve plate ( 12 ) is formed of iron-based materials such as cast iron or steel. Then, the sliding surface ( 12 A) which is the front side of the valve plate ( 12 ) is covered with the sliding layer ( 21 ) formed of a sintered copper alloy containing Cu (copper) and Sn (tin) as principal components and the remaining components as the remainder. The remainder has 2 to 6 wt % CaF 2  (calcium fluoride) as an essential component, and an average particle size of said CaF 2  is controlled to fall within the range from 40 μm to 350 μm. A sliding surface ( 8 A) of a cylinder block ( 8 ) which is a opposing part sliding surface is not covered with the copper-alloy sliding layer ( 21 ) but is covered with a sliding layer of iron-and-steel based materials.

TECHNICAL FIELD

The present invention relates to a hydraulic rotary machine used suitably as a hydraulic pump or a hydraulic motor installed on construction machines, such as hydraulic excavators, hydraulic cranes, wheel loaders and the like, and on various kinds of industrial machinery.

BACKGROUND ART

In general, construction machines, such as hydraulic excavators, hydraulic cranes, wheel loaders and the like, are equipped with hydraulic rotary machines, such as hydraulic pumps used as a hydraulic pressure source of hydraulic equipment, hydraulic motors used as a drive source for traveling or revolving, and the like. The hydraulic rotary machine is configured of, for example, a swash-plate, bent-axis or radial-piston hydraulic rotary machine, and the like. In this case, examples of the swash-plate or bent-axis hydraulic rotary machine which is an axial-piston hydraulic rotary machine include the fixed displacement type and the variable displacement type.

A hydraulic rotary machine of this kind according to the conventional art includes, for example: a hollow casing; a rotational shaft rotatably provided in the casing; a cylinder block placed inside the casing to rotate together with the rotational shaft, the cylinder block being provided with a plurality of cylinders formed therein to be spaced in the circumferential direction, and cylinder ports formed to open on an end face in positions corresponding to the respective cylinders; and a plurality of pistons that are inserted into the respective cylinders of the cylinder block to be capable of reciprocating therein (Patent Document 1).

Here, in the hydraulic rotary machine according to Patent Document 1, a sliding layer made of a low-friction copper alloy is formed on a sliding surface between two members sliding on each other, e.g., a sliding surface between a cylinder and a piston. Specifically, the sliding layer is made of a low-friction copper alloy containing 0.5 to 15 wt % FeMo (Ferromolybdenum) with the aim of achieving a reduction in coefficient friction, a reduction in sliding resistance, a reduction of the amount of wear, a compatibility enhancement and an efficiency improvement.

On the other hand, Patent Document 2 discloses the configuration of forming a sliding layer of a bronze based alloy containing 5 wt % or more Mo (Molybdenum) using thermal spray coating techniques with the aim of improvements in properties of seizure resistance and wear resistance.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Patent Laid-Open No. Hei 7-167041 A

Patent Document 2: Japanese Patent Laid-Open No. 2004-346417 A (Japanese Patent No. 4289926 B)

SUMMARY OF THE INVENTION

With the hydraulic rotary machine disclosed in Patent Document 1, the sliding layer is formed of a copper alloy containing hard particles of FeMo and/or the like for an improvement in seizure resistance properties. On the other hand, with the hydraulic rotary machine disclosed in Patent Document 2, the sliding layer is formed of a hard copper alloy containing Mo for an improvement in seizure resistance properties. In the case of such configurations, the hard particles contained in the sliding layer may possibly damage materials of a sliding opposing part, for example, when the hydraulic rotary machine is rotated at high speed or operated at high contact pressure or when a shortage of an oil-film occurs on a sliding area. On the other hand, the hard copper alloy forming the sliding layer may possibly damage materials of a sliding opposing part.

On the other hand, the hydraulic rotary machine has, in the drive process, the possibilities of causing a pressure difference due to switching of a supply and discharge port, causing passage of pressurized oil through a notch or a throttle part, causing variations in pressure of the pressurized oil from the supply and discharge port, and causing a negative pressure. In this case, due to impact of jets or bubble burst, damage to the copper alloy, known as so-called cavitation erosion, is likely to occur in an oil passage through which pressurized oil flows in the hydraulic rotary machine.

In this case, progression of wear and an outflow of wear powder which will result in contamination (contaminants) may possibly cause a reduction in performance of the hydraulic rotary machine and the occurrence of noise therein. To avoid this, the copper alloy of the sliding layer disposed in the oil passage through which pressurized oil flows is desirably capable of ensuring mechanical strength correlating with the amount of cavitation erosion, in addition to ensuring seizure resistance properties.

The present invention is made in view of the above-described disadvantageous problems in the conventional art, and it is an object of the present invention to provide a hydraulic rotary machine capable of achieving compatibility between ensuring seizure resistance properties and ensuring mechanical strength (cavitation erosion resistance properties) of a sliding layer.

(1) The present invention is applied to a hydraulic rotary machine comprising: first members that include first sliding surfaces; and second members that include second sliding surfaces sliding with respect to the first sliding surfaces, wherein one ends of oil passages, through which an hydraulic oil flows, open on at least any of the first sliding surfaces and the second sliding surfaces.

In order to solve the aforementioned problems, a characteristic of a configuration adopted by the present invention is that a sliding layer formed of a sintered copper alloy is formed on one of the first sliding surfaces and the second sliding surfaces; the sliding layer has a composition including Cu and Sn as principal components and the remainder as remaining components; the remainder includes 2 wt % to 6 wt % CaF₂ as an essential component, and an average particle size of the CaF₂ is controlled to fall within a range from 40 μm to 350 μm; and the other sliding surface of the first sliding surface and the second sliding surface is formed of a sliding layer of iron-and-steel materials.

With this arrangement, the sintered copper alloy formed as the sliding layer for one of the sliding surfaces is a copper alloy (bronze alloy) containing Cu (copper) and Sn (tin) as principal components, and CaF₂ (calcium fluoride) as an essential component of the remainder. In this case, CaF₂ is controlled to be 2 wt % or more and 6 wt % or less and to have an average particle size of from 40 μm or more to 350 μm or less. As a result, the CaF₂ particles scattered in the inside (within the copper alloy) makes it possible to ensure the mechanical strength (material strength, cavitation erosion resistance properties). In addition, the CaF₂ particles scattered on the surface (sliding surface) break away from the surface to create holes on the surface, so that the holes function as oil sumps. On the other hand, the CaF₂ particles remaining on the surface function as a solid lubricant in relation to the opposing part surface. In consequence, the seizure resistance properties can be ensured.

It should be noted that, when the CaF₂ content is less than 2 wt %, the number of CaF₂ particles scattered on the surface is smaller. This causes the deterioration of the function as the oil sumps caused by the breaking-away of the CaF₂ particles and the function as the solid lubricant of the CaF₂ particles remaining on the surface, so that the seizure resistance properties may not be easily ensured. On the other hand, when the CaF₂ content is increased, the oil sumps and the solid lubricant can be increased to cause an improvement in seizure resistance properties. However, when the CaF₂ content exceeds 6 wt %, an increase in the content of CaF₂ with low toughness and an increase in the CaF₂ grain boundaries combine may possibly reduce the cavitation erosion resistance properties (increase the wear).

Even with the CaF₂ content of 2 to 6 wt %, when, for example, the CaF₂ average particle size is less than 40 μm, the grain boundaries between CaF₂ and metal (copper) increase on the surface of the sliding layer, causing the likelihood of a reduction in cavitation erosion resistance properties (increase in wear). On the other hand, when CaF₂ average particle size exceeds 350 μm, for example, the number of holes 24 caused by breaking-away of the CaF₂ particles is decreased, causing the likelihood of a reduction in seizure resistance properties.

By contrast, according to the present invention, since CaF₂ is controlled to be 2 to 6 wt % and to have an average particle size of 40 μm to 350 μm, the CaF₂ particles can be distributed in the inside of and on the surface of the sliding layer in balance, thus achieving the compatibility between ensuring the seizure resistance properties and ensuring the mechanical strength (cavitation erosion resistance properties).

(2) According to the present invention, the remainder of the sliding layer has a composition including at least one component or more selected from the group consisting of Pb, Ni, Be, P, Fe, Zn, Al, Si, Mn, Mg, S, Ti, V, Cr and W, in addition to the CaF₂ as the essential component.

With this configuration, the remainder of the sintered copper alloy has a composition including at least one component or more selected from the group consisting of Pb (lead), Ni (nickel), Be (beryllium), P (phosphorus), Fe (iron), Zn (zinc), Al (aluminum), Si (silicon), Mn (manganese), Mg (magnesium), S (sulfur), Ti (titanium), V (vanadium), Cr (chromium) and W (tungsten), in addition to CaF₂ as the essential component. This makes it possible to provide the compatibility between ensuring the seizure resistance properties and ensuring the mechanical strength at a higher level.

For example, when the composition includes Pb, the amount of Pb component exceeding a solubility limit of the copper alloy is dispersed in the matrix. Because of this, when a state in which seizure occurs during sliding (the surface temperature is higher than the melting point of Pb) takes place, the Pb located around the sliding surface melts and escapes, making it possible to achieve a seizure reduction. As a result, in addition to the effect of improving the seizure resistance properties that is brought about by CaF₂, the seizure reduction effect brought about by Pb can be obtained. Therefore, a synergistic effect of both the effects can bring about a further improvement in seizure resistance properties.

For example, when a composition does not include Pb and includes at least any selected from the group consisting of Ni, Be, P, Fe, Zn, Al, Si, Mn, Mg, S, Ti, V, Cr, and W, the hardness of the copper alloy can be increased, producing an improvement in the mechanical strength. Further, when a composition includes Pb as well as at least any selected from the group consisting of Ni, Be, P, Fe, Zn, Al, Si, Mn, Mg, S, Ti, V, Cr, and W, the seizure resistance properties and the mechanical strength can both be improved.

(3) In this respect, according to the present invention, a composition of the principal components of the sliding layer includes 11 wt % to 13 wt % (11 wt % or more and 13 wt % or less) of the Sn in addition to the Cu; and a composition of the remainder of the sliding layer includes 4 wt % to 6 wt % (4 wt % or more and 6 wt % or less) of the Ni in addition to the CaF₂. This makes it possible to increase the hardness of the copper alloy, leading to an improvement in mechanical strength.

(4) Further, according to the present invention, a composition of the principal components of the sliding layer includes 11 wt % to 13 wt % (11 wt % or more and 13 wt % or less) of the Sn in addition to the Cu; and a composition of the remainder of the sliding layer includes 1 wt % to 3 wt % (1 wt % or more and 3 wt % or less) of the Pb and 4 wt % to 6 wt % (4 wt % or more and 6 wt % or less) of the Ni in addition to the CaF₂. This makes it possible to improve both the seizure resistance properties and the mechanical strength.

(5) According to the present invention, the remainder of the sliding layer includes Pb and Ni as essential components in addition to the CaF₂ as the essential component, and the CaF₂ is controlled to include 90 wt % to 100 wt % of the CaF₂ having particle sizes falling within the range from 40 μm to 350 μm.

With this configuration, the remainder of the sintered copper alloy includes CaF₂, Pb and Ni as essential components, and the CaF₂ contained in the sintered copper alloy is controlled such that 90 wt % or more and 100 wt % or less of the CaF₂ have particle sizes falling within a range of 40 μm or more and 350 μm or less. This brings about an improvement in quality control for mass production in addition to the compatibility between ensuring the seizure resistance properties and ensuring the mechanical strength at a higher level.

That is, a seizure reduction can be achieved by containing Pb as an essential component, and also an improvement in mechanical strength can be achieved by containing Ni as an essential component. Further, the control of CaF₂ particle size is performed such that 90 wt % or more and 100 wt % or less of the CaF₂ have particle sizes in the range from 40 μm or more to 350 μm or less. This makes it possible to inhibit the hole of a size exceeding 350 μm from being formed on the surface of the sliding layer by the breaking-away of CaF₂. This facilitates discrimination between cavities or pin holes of 500 μm or greater which are regarded as defects of a sintered alloy, and the hole caused by the breaking-away of CaF₂, leading to an improvement in quality control for mass production.

(6) According to the present invention, the hydraulic rotary machine comprises: a hollow casing; a rotational shaft that is rotatably mounted inside the casing; a cylinder block that is placed inside said casing to rotate together with the rotational shaft, the cylinder block being provided with a plurality of cylinders formed therein to be spaced in a circumferential direction and extend in an axial direction, and cylinder ports formed to open on an end face in positions corresponding to the respective cylinders; a plurality of pistons that are inserted into the respective cylinders of the cylinder block to be capable of reciprocating therein; and a valve plate that is placed between the casing and the cylinder block and includes supply and discharge ports formed to communicate with the respective cylinders through the cylinder ports, wherein the first member comprises the valve plate that includes the supply and discharge ports formed to be the oil passages; and the second member comprises the cylinder block sliding on the valve plate and including the cylinder ports formed to be the oil passages.

With this arrangement, the sliding layer formed of the aforementioned sintered copper alloy is formed on one of the mutually sliding surfaces of the valve plate which is the first member and the cylinder block which is the second member. Thus, ensuring the seizure resistance properties and ensuring the mechanical strength can be achieved in the sliding area between the valve plate and the cylinder block. As a result, as compared with the conventional art, the operation of the hydraulic rotary machine is made possible at higher rpm and higher pressure, leading to downsizing and an increase in output of the hydraulic rotary machine. Further, along with the improvement of the seizure resistance properties, an increase in contact pressure in the sliding area is made possible. This makes it possible to reduce the amount of leakage from the sliding area, leading to greater efficiency.

(7) According to the present invention, the hydraulic rotary machine comprises: a hollow casing; a rotational shaft that is rotatably mounted inside the casing; a cylinder block that is placed inside the casing to rotate together with the rotational shaft, the cylinder block being provided with a plurality of cylinders formed therein to be spaced in a circumferential direction and extend in an axial direction, and cylinder ports formed to open on an end face in positions corresponding to the respective cylinders; a plurality of pistons that are inserted into the respective cylinders of the cylinder block to be capable of reciprocating therein and include first oil supply ports formed therein; a valve plate that is placed between the casing and the cylinder block and includes supply and discharge ports formed to communicate with the respective cylinders through the cylinder ports; a plurality of shoes that are mounted to projecting ends of the respective pistons to be capable of tilting around and include second oil supply ports formed therein to be connected to the first oil supply ports; and a swash plate that is placed on the opposite side of the cylinder block from the valve plate and on which the respective shoes slide, wherein the first member comprises each of the shoes including the second oil supply port formed to be said oil passage; and the second member comprises the swash plate on which each of the shoes slides.

With this arrangement, the sliding layer formed of the aforementioned sintered copper alloy is formed on one of the mutually sliding surfaces of each shoe plate which is the first member and the swash plate which is the second member. Thus, ensuring the seizure resistance properties and ensuring the mechanical strength can be achieved in the sliding area between each shoe and the swash plate. As a result, it is possible to achieve downsizing, an increase in output, and an increase in efficiency of the swash-plate type hydraulic rotary machine.

(8) According to the present invention, the hydraulic rotary machine comprises: a hollow casing; a rotational shaft that is rotatably mounted inside the casing; a cylinder block that is placed inside the casing to rotate together with the rotational shaft, the cylinder block being provided with a plurality of cylinders formed therein to be spaced in a circumferential direction, and cylinder ports formed to open on an end face in positions corresponding to the respective cylinders; and a plurality of pistons that are inserted into the respective cylinders of the cylinder block to be capable of reciprocating therein, wherein the first member comprises the cylinder block including the cylinder ports formed to be the oil passages; and the second member comprises the pistons sliding with respect to the cylinders of the cylinder block.

With this arrangement, the sliding layer formed of the aforementioned sintered copper alloy is formed on one of the mutually sliding surfaces of the cylinder block which is the first member and the piston which is the second member. Thus, ensuring the seizure resistance properties and ensuring the mechanical strength can be achieved in the sliding area between the cylinder block and the piston. As a result, it is possible to achieve downsizing, an increase in output, and an increase inefficiency of the hydraulic rotary machine.

(9) According to the present invention, the hydraulic rotary machine comprises: a hollow casing; a rotational shaft that is rotatably mounted inside the casing; a cylinder block that is placed inside said casing to rotate together with the rotational shaft, the cylinder block being provided with a plurality of cylinders formed therein to be spaced in a circumferential direction and extend in an axial direction, and cylinder ports formed to open on an end face in positions corresponding to the respective cylinders; a plurality of pistons that are inserted into the respective cylinders of the cylinder block to be capable of reciprocating therein; a valve plate that is placed between the casing and the cylinder block and includes supply and discharge ports formed to communicate with the respective cylinders through the cylinder ports; a plurality of shoes that are mounted to projecting ends of said respective pistons to be capable of tilting around; a swash plate that includes one end face facing the cylinder block to allow each of the shoes to slide thereon and the other end face on which a convex-curved sliding surface is formed, and is tiltably mounted to tilt about a swash-plate supporting point; and a swash plate support member that includes a concave-curved tilting slide surface formed to allow the sliding surface of the swash plate to slide thereon, and an oil supply port formed therein for passage of the hydraulic oil supplied from the cylinder ports, wherein the first member comprises the swash plate support member including the oil support port formed therein to be the oil passage; and the second member comprises the swash plate sliding with respect to the swash plate support member.

With this arrangement, the sliding layer formed of the aforementioned sintered copper alloy is formed on one of the mutually sliding surfaces of the swash plate support member which is the first member and the swash plate which is the second member. Thus, ensuring the seizure resistance properties and ensuring the mechanical strength can be achieved in the sliding area between the swash plate support member and the swash plate. As a result, it is possible to achieve downsizing, an increase in output, and an increase in efficiency of the variable-displacement type and swash-plate type hydraulic rotary machine.

(10) According to the present invention, the hydraulic rotary machine comprises: a hollow casing; a rotational shaft that is rotatably mounted inside the casing and includes a drive disk at a top end; a cylinder block that is placed inside the casing to rotate together with the rotational shaft, the cylinder block being provided with a plurality of cylinders formed therein to be spaced in a circumferential direction and extend in an axial direction, and cylinder ports formed to open on an end face in positions corresponding to the respective cylinders; a plurality of pistons that are inserted into the respective cylinders of the cylinder block to be capable of reciprocating therein, and include projecting ends supported by the drive disk of the rotational shaft to be capable of tilting therein; a valve plate that includes one end face facing the cylinder block to allow the cylinder block to slide thereon and the other end face on which a convex-curved sliding surface is formed, and is tiltably mounted to tilt together with the cylinder block about a valve-plate supporting point; and a head cover that includes a concave-curved tilting slide surface to allow the sliding surface of the valve plate to slide on, wherein the first member comprises the valve plate including supply and discharge ports formed to be the oil passages communicating with the respective cylinders through the cylinder ports; and the second member comprises the head cover on which the valve plate slides.

With this arrangement, the sliding layer formed of the aforementioned sintered copper alloy is formed on one of the mutually sliding surfaces of the valve plate which is the first member and the head cover (valve plate support member) which is the second member. Thus, ensuring the seizure resistance properties and ensuring the mechanical strength can be achieved in the sliding area between the valve plate and the head cover. As a result, it is possible to achieve downsizing, an increase in output, and an increase in efficiency of the variable-displacement type and bent-axis type hydraulic rotary machine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical section view showing a fixed-displacement type and swash-plate type hydraulic rotary machine according to a first embodiment of the present invention.

FIG. 2 is a composition structure diagram schematically showing the surface of one sliding surface (the sliding surface of a valve plate) after finishing machining processes.

FIG. 3 is a composition structure diagram schematically showing the surface of one sliding surface (the sliding surface of a valve plate) after a breaking-in period.

FIG. 4 is a composition structure diagram schematically showing the surface of one sliding surface (the sliding surface of a valve plate) after finishing machining processes as a cross section of FIG. 2.

FIG. 5 is a composition structure diagram schematically showing the surface of one sliding surface (the sliding surface of a valve plate) after a breaking-in period as a cross section of FIG. 3.

FIG. 6 is a characteristic chart showing the relationship between CaF₂ average particle sizes when the CaF₂ content is 3 wt % and motor drive pressures when seizure limit is reached, in comparison with the conventional art.

FIG. 7 is a characteristic chart showing the relationship between CaF₂ percentage by weight when the CaF₂ average particle size is 100 μm and test pressures when seizure limit is reached, in comparison with the conventional art.

FIG. 8 is a characteristic chart showing the relationship between CaF₂ average particle sizes when the CaF₂ content is 3 wt % and test pressures when seizure limit is reached, in comparison with the conventional art.

FIG. 9 is a characteristic chart showing the relationship between CaF₂ percentage by weight when the CaF₂ average particle size is 100 μm and the amount of cavitation erosion, in comparison with the conventional art.

FIG. 10 is a characteristic chart showing the relationship between CaF₂ average particle sizes when the CaF₂ content is 3 wt % and the amount of cavitation erosion, in comparison with the conventional art.

FIG. 11 is a vertical section view showing a variable-displacement type and swash-plate type hydraulic rotary machine according to a second embodiment of the present invention.

FIG. 12 is a section view of the hydraulic rotary machine as viewed in the direction of arrows XII-XII in FIG. 11.

FIG. 13 is a vertical section view showing a variable-displacement type and bent-axis type hydraulic rotary machine according to a third embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of a hydraulic rotary machine according to the present invention will be explained in detail with reference to the accompanying drawings by taking the case of application to an axial-piston hydraulic rotary machine as an example.

FIG. 1 to FIG. 10 show a first embodiment according to the present invention. In the drawings, indicated at 1 is a hydraulic rotary machine employed in the first embodiment, more specifically, a fixed-displacement type, swash-plate type hydraulic motor (hereinafter referred to as a “hydraulic motor 1”) that is driven by a supply of operating oil which is a representative example of a hydraulic oil. Indicated at 2 is a hollow casing forming a shell of the hydraulic motor 1. The casing 2 includes a casing body 3 formed in a bottomed cylinder shape with an opening part 3A and a bottom part 3B, and a lid member 4 covering the opening part 3A of the casing body 3.

The bottom part 3B of the casing body 3 has an inclined surface 3C formed at an inclination with respect to the axis of a rotational shaft 5 which will be described later. The lid member 4 of the casing 2 has a pair of supply/discharge passages 4A, 4B formed therein. The supply/discharge passages 4A, 4B are connected via, for example, a directional control valve and the like to a hydraulic pressure source (none shown). In this case, for example, when high-pressurized oil (motor driving pressure) is supplied from one supply/discharge passages 4A of the supply/discharge passages 4A, 4B, the other supply/discharge passages 4B operate as a low pressure side to discharge return oil flowing from the hydraulic motor toward a tank.

The rotational shaft 5 is rotatably placed in the casing 2 to extend in the axial direction. The rotational shaft 5 has one end in the axial direction (right end in FIG. 1) rotatably mounted via a bearing 6 to the bottom part 3B of the casing body 3. The other end (left end in FIG. 1) of the rotational shaft 5 is rotatably mounted via a bearing 7 to the lid member 4.

A cylinder block 8 is placed in the casing 2 to be capable of rotating through the rotational shaft 5. The cylinder block 8 is mounted to be splined to the outer periphery of the rotational shaft 5, rotating together with (integrally with) the rotational shaft 5. One (on the right side in FIG. 1) of the end faces of the cylinder block 8 faces a swash plate 14 to be described later. The other end face (on the left side in FIG. 1) of the cylinder block 8 serves as a sliding surface (switching sliding surface) 8A sliding on a sliding surface 12A of a valve plate 12 to be described later. In the cylinder block 8, a cylinder 9 to be described later is formed in conjunction with a cylinder port 10.

A plurality of cylinders 9 are independently formed (bored) in the cylinder block 8. Each of the cylinders 9 are spaced at regular intervals around the rotational shaft 5 in the circumferential direction of the cylinder block 8, and extend in the axial direction of the cylinder block 8. One end (the right end in FIG. 1) of each of the cylinders 9 opens on an end face of the cylinder block 8. In the other end (the left end in FIG. 1) of each cylinder 9, the cylinder port 10 is formed. The inner surface of each cylinder 9 is formed as a sliding surface 9A on which a sliding surface 11B of a piston 11 to be described later slides. The cylinder port 10 is formed (bored) in a position corresponding to each cylinder 9 to open on the sliding surface 8A of the cylinder block 8. The cylinder port 10 communicates intermittently with each of supply and discharge ports 12B, 12C of the valve plate 12 to be described later.

A plurality of the pistons 11 each are inserted into each of the cylinders 9 to be capable of reciprocating therein. Each of the pistons 11 is slidingly displaced (reciprocates) in each of the cylinders 9 by, for example, a supply/discharge of pressurized oil into/from each of the cylinders 9 through each of the cylinder ports 10 from/to each of the supply/discharge passages 4A, 4B. At this time, based on the sliding displacement, each of the pistons 11 produces a rotating force acting on the cylinder block 8 to rotate about the rotational shaft 5.

One end (the right end in FIG. 1) of each of the pistons 11 in the axial direction projects from the cylinder 9 toward the swash plate 14 to be described later, and the projecting end is formed as a spherical part 11A. A shoe 13 to be described later is fitted to the spherical part 11A. The outer peripheral surface of each of the pistons 11 is formed as a sliding surface 11B sliding on the sliding surface 9A which is the inner surface of the corresponding cylinder 9. A first oil supply port 11C through which the hydraulic oil (operating oil) flows in the cylinder 9 is formed inside each of the pistons 11 to extend in the axial direction. The first oil supply port 11C is provided to supply the hydraulic oil within the cylinder 9 as lubricating oil to a sliding area between the shoe 13 and the swash plate 14 through a second oil supply port 13B formed in the shoe 13.

The valve plate 12 is placed between the lid member 4 of the casing 2 and the cylinder block 8. The valve plate 12 is formed in a disk shape and fixedly attached to the lid member 4. The valve plate 12 has one end face (the right end face in FIG. 1) that faces the cylinder block 8 and is formed as the sliding surface 12A on which the sliding surface 8A of the cylinder block 8 slides. A pair of supply and discharge ports 12B, 12C are formed in the valve plate 12 such that piston top dead center and piston bottom dead center are located between the supply and discharge ports 12B, 12C. The supply and discharge ports 12B, 12C are provided for passage of the hydraulic oil flowing between the cylinder 9 and the supply/discharge passages 4A, 4B of the lid member 4. One ends (the right ends in FIG. 1) of the supply and discharge ports 12B, 12C open on the sliding surface 12A to communicate with the cylinders 9 through the cylinder ports 10. The other ends (the left ends in FIG. 1) of the supply and discharge ports 12B, 12C communicate with the respective supply/discharge passages 4A, 4B of the lid member 4.

The shoe 13 is mounted to the spherical part 11A which is the projecting end of each of the pistons 11 to be capable of tilting around. Each of the shoes 13 has a sliding surface 13A sliding on a sliding surface 14A of the swash plate 14 to be described later. Each of the shoes 13 is pressed against the sliding surface 14A of the swash plate 14 by the piston 11, thus sliding on the sliding surface 14A along a ring-shaped locus with rotation of the cylinder block 8.

Each of the shoes 13 has the second oil supply port 13B formed to extend through the inside of the shoe 13 and connected to the first oil supply port 11C of the corresponding piston 11. The second oil supply port 13B is provided for the hydraulic oil flowing from the first oil supply port 11C, and one end (the right end in FIG. 1) of the second oil supply port 13B opens on the sliding surface 13A. As a result, the hydraulic oil in the cylinder 9 is supplied to the sliding area between the shoe 13 and the swash plate 14 through the first oil supply port 11C and the second oil supply port 13B.

The swash plate 14 is placed on the opposite side of the cylinder block 8 from the valve plate 12 to face the cylinder block 8. After the rotational shaft 5 is inserted through a central portion of the swash plate 14, the swash plate 14 is placed in a slanting position between the bottom part 3B of the casing body 3 and the cylinder block 8 (with being inclined along the inclined surface 3C of the bottom part 3B). The surface of the swash plate 14 facing the cylinder block 8 is formed as a sliding surface 14A on which the sliding surface 13A of each of the shoes 13 slides.

A shoe retainer 15 is provided to regulate the position of each of the shoes 13. The shoe retainer 15 is formed in a ring shape. A retainer ball 16 is fitted to one end (the right end in FIG. 1) of the cylinder block 8. The outer peripheral surface of the retainer ball 16 is formed in a spherical surface shape to be fitted to the inner peripheral surface of the shoe retainer 15. A pressing spring 17 is located in the cylinder block 8 to be mounted between the retainer ball 16 and the cylinder block 8. The pressing spring 17 presses each of the shoes 13 against the swash plate 14 through the retainer ball 16 and the shoe retainer 15. In addition, the pressing spring 17 presses the sliding surface 8A of the cylinder block 8 against the valve plate 12.

Next, an operation of the hydraulic motor 1 according to the first embodiment will be described.

The pressurized oil supplied from the hydraulic pressure source (hydraulic pump) is guided to the supply/discharge passages 4A serving as supply passages formed in the lid member 4. The pressurized oil guided into the supply/discharge passages 4A is supplied into the cylinder 9 through the supply and discharge port 12B serving as a supply port formed in the valve plate 12, and the cylinder port 10 of the cylinder block 8. As a result, the pressurized oil in the cylinder 9 presses the piston 11 to press the shoe 13 through the piston 11 against the sliding surface 14A of the swash plate 14. The piston 11 rotates the cylinder block 8 by a reaction to the pressing force, so that the rotational shaft 5 is driven to rotate together with the cylinder block 8. At this time, the pressurized oil supplied into the cylinder 9 is returned to the tank through the cylinder port 10, the supply and discharge port 12C serving as a discharge port formed in the valve plate 12, and the supply/discharge passages 4B serving as discharge passages formed in the lid member 4.

Next, an explanation will be made of a sliding layer 21 formed of sintered metal (see FIG. 2 to FIG. 5), which is a feature of the first embodiment.

Specifically, during the operation in the hydraulic motor 1, the cylinder 9 of the cylinder block 8 serving as “a first member” and the piston 11 serving as “a second member” slide with each other. In addition to this, the valve plate 12 serving as “a first member” and the cylinder block 8 serving as “a second member” slide with each other. Further, the shoe 13 serving as “a first member” and the swash plate 14 serving as “a second member” slide with each other.

In this case, a first set of “a first sliding surface and a second sliding surface” will be described. The cylinder block 8 has the sliding surface 9A of the cylinder 9 serving as “the first sliding surface”, while the piston 11 has the sliding surface 11B serving as “the second sliding surface”, in which the cylinder port 10 serving as “an oil passage” opens on the sliding surface 9A of the cylinder 9. A second set of “a first sliding surface and a second sliding surface” will be described. The valve plate 12 has the sliding surface 12A serving as “the first sliding surface”, while the cylinder block 8 has the sliding surface 8A serving as “the second sliding surface”, in which the supply and discharge ports 12B, 12C serving as “oil passages” open on the sliding surface 12A of the valve plate 12, while the cylinder port 10 serving as “an oil passage” opens on the sliding surface 8A of the cylinder block 8. A third set of “a first sliding surface and a second sliding surface” will be described. The shoe 13 has the sliding surface 13A serving as “the first sliding surface”, while the swash plate 14 has the sliding surface 14A serving as “the second sliding surface”, in which the second oil supply port 13B serving as “an oil passage” opens on the sliding surface 13A of the shoe 13. That is, the hydraulic oil (operating oil) is supplied through “the oil passages” to all the sliding areas between “the first sliding surface and the second sliding surface” which are the sliding area of the hydraulic motor 1.

In the case of the first embodiment, the following description will be given of the configuration of at least one set of “the first sliding surface and the second sliding surface” of the three sets of “the first sliding surfaces and the second sliding surfaces”. It should be noted that in the following description, the sliding surface 12A of the valve plate 12 is used as a representative example of “the first sliding surface”, while the sliding surface 8A of the cylinder block 8 is used as a representative example of “the second sliding surface”.

In the case of the first embodiment, the sliding layer 21 made of a sintered copper alloy as shown in FIG. 2 to FIG. 5 is formed on one sliding surface of the sliding surface 12A of the valve plate 12 and the sliding surface 8A of the cylinder block 8, for example, on the sliding surface 12A of the valve plate 12. Namely, the valve plate 12 is formed of iron based materials such as cast iron, steel or the like, and the sliding surface 12A which is the surface of the valve plate 12 is made of a sintered copper alloy having a composition of Cu (copper) and Sn (tin) as principal components and the remainder as the other components. The principal components (Cu and Sn) and the remainder add up to 100 wt %. In this respect, the remainder includes 2 to 6 wt % (2 wt % or more and 6 wt % or less) of CaF₂ (calcium fluoride) as an essential component and an average particle size of CaF₂ is controlled to fall within the range from 40 μm to 350 μm (40 μm or larger and 350 μm or smaller). In this case, for the sintered copper alloy, the percentage by weight of the remainder including CaF₂ as an essential component is added to the percentages by weight of Cu and Sn as the principal components to amount to 100 wt % in total.

On the other hand, the other sliding surface of the sliding surface 12A of the valve plate 12 and the sliding surface 8A of the cylinder block 8, for example, the sliding surface 8A of the cylinder block 8 is configured of a sliding layer made of iron-and-steel based materials. Specifically, the cylinder block 8 is formed of iron based materials such as cast iron, steel or the like, and has undergone nitriding heat treatment or carburizing heat treatment, and also surface treatment or coating treatment as necessary. In other words, the sliding layer 21 made of a copper alloy as described above is not formed on the sliding surface 8A of the cylinder block 8.

Here, the remainder of the sintered copper alloy formed as the sliding layer 21 on one sliding surface (the sliding surface 12A of the valve plate 12) of the two sliding surfaces preferably includes, in addition to CaF₂ as the essential component, at least one or more selected from the group consisting of Pb (lead), Ni (nickel), Be (beryllium), P (phosphorus), Fe (iron), Zn (zinc), Al (aluminum), Si (silicon), Mn (manganese), Mg (magnesium), S (sulfur), Ti (titanium), V (vanadium), Cr (chromium) and W (tungsten). For example, the sintered copper alloy may contain Cu and Sn as principal components, and Sn of the principal components may be 11 to 13 wt % (11 wt % or more and 13 wt % or less). The Cu component of the principal components is desirably 50 wt % or more and 90 wt % or less. On the other hand, the remaining components other than the principal components, namely, the remainder, can include 4 to 6 wt % (4 wt % or more and 6 wt % or less) of Ni and 2 to 6 wt % (2 wt % or more and 6 wt % or less) of CaF₂ as essential components. In this case, the percentage by weight of the remainder including CaF₂ and Ni as the essential components is added to the percentages by weight of Cu and Sn as the principal components to amount to 100 wt % in total.

More preferably, the remainder of the sintered copper alloy formed as the sliding layer 21 includes Pb and Ni as essential components in addition to CaF₂ as the essential component. For example, the sintered copper alloy may contain Cu and Sn as the principal components of which Sn is 11 to 13 wt % (11 wt % or more and 13 wt % or less). On the other hand, the remaining components other than the principal components, namely, the remainder can include 1 to 3 wt % (1 wt % or more and 3 wt % or less) of Pb, 4 to 6 wt % (4 wt % or more and 6 wt % or less) of Ni and 2 to 6 wt % (2 wt % or more and 6 wt % or less) of CaF₂ as essential components. In this case, the percentage by weight of the remainder including CaF₂, Ni and Pb as the essential components is added to the percentages by weight of Cu and Sn as the principal components to amount to 100 wt % in total.

Further, CaF₂ contained in the sintered copper alloy is controlled such that 90 to 100 wt % (90 wt % or more and 100 wt % or less) of the CaF₂ have an average particle size falling within the range from 40 μm to 350 μm (40 μm or larger and 350 μm or smaller). In this case, the controlling of CaF₂ particle size can be managed by, for example, passing the CaF₂ powder through a mesh screen.

The sliding layer 21 made of such a sintered copper alloy is manufactured by powder metallurgy. A concrete method of manufacturing will be described. Initially, raw materials of the sintered copper alloy having Cu and Sn as the principal components are mechanically blended to produce uniform mixed powder. For the metal composition of the mixed powder, in addition to CaF₂ which is an essential component of the remainder, one kind or more of a single element or an alloy of elements selected from the group consisting of Pb, Ni, Be, P, Fe, Zn, Al, Si, Mn, Mg, S, Ti, V, Cr, W and the like which are able to be produced by powder metallurgy, can be added as necessary. However, the components of Mg, S, Ti, V, Cr and W have no intended effects but are addable, which may be added by a percentage by weight to the extent that opposing part materials do not suffer damage. The total of Be, P, Fe, Zn, Al, Si, Mn, Mg, S, Ti, V, Cr and W is desirably less than 5 wt %, specifically, zero wt % or more and 5 wt % or less.

The mixed powder is put into a die of, for example, a shape corresponding to the sliding surface 12A of the valve plate 12, which is then compacted at a pressure of 0.5 to 5 MPa (0.5 MPa or greater and 5 MPa or less) to form a compact corresponding to the sliding layer 21 before being sintered. The compact may be formed by use of CIP (Cold Isostatic Pressing). On the other hand, a base-metal, on the surface of which the sliding layer 21 of the sintered copper alloy is formed, is plated on its surface with Cu after, for example, steel materials are formed (worked) into a shape of the valve plate 12. The above-described compact is placed on the Cu-plated steel material (base-metal), which is then placed in a reducing gas atmosphere in a sintering furnace, heated to a temperature of 500 to 900° C. (500° C. or higher and 900° C. or lower), and maintained at a predetermined temperature for 0.5 to 4 hours (0.5 hours or longer and 4 hours or shorter). This causes the compact to be sintered and at the same time the compact to be diffusion-bonded to the Cu-plated steel material (base-metal). As a result, the member (valve plate 12) with the sliding layer 21 of the sintered copper alloy being formed on the surface can be produced.

In the sintering process, the application of press is desirable. When the press is applied, adhesion between the sintered copper alloy and the base-metal can be improved. In another producing method, the Cu-plated steel material (base-metal) is placed in a carbon mold, and then the mixed powder is packed on the Cu-plated steel material, which is then sintered. In this case, the mixed powder is pressurized by use of a carbon pin or the like.

Methods employed as a sintering method may include, in addition to the sintering by means of heating, hot-pressing (heating and pressurizing), electric current sintering, plasma sintering, and the like. Using such a sintering method makes it possible to fabricate the sliding layer 21 with a relative density of 95% or more. Further, HIP (Hot Isostatic Pressing) or the like can be used to increase the relative density.

Incidentally, in most cases, the sintered members fabricated by powder metallurgy undergo quality control for mass production with cavities or pin holes of 500 μm or greater being regarded as defects.

Next, an explanation will be made of components of a copper alloy containing Cu and Sn as principal components. Sn as the principal component diffuses into Cu in the sintering process to promote the sintering, resulting in a component forming a bronze alloy. In most cases, Sn is contained in the range of 5 to 15 wt % (5 wt % or more and 15 wt % or less). When this content is too lower, the degree of sintering is likely to be insufficient to decrease the mechanical strength for the structure. In addition to this, the diffusion bonding to the Cu plating on the steel material is likely to be stopped to cause an inadequate bonding strength. On the other hand, when the content is too larger, segregation and pores are likely to occur to give rise to structure weakening, possibly leading to a reduction in mechanical strength and deterioration of the sliding properties.

In regard to the content of Pb of a component in the remainder, when it exceeds 10 wt %, it melts in the sintering process to generate shrinkage cavities, thus possibly causing a reduction in strength. To avoid this, the Pb content can be, for example, zero to 10 wt % (zero wt % or more and 10 wt % or less). Regarding to the content of Ni of a component in the remainder, Ni has the properties to imparting mechanical strength, but it is inactive when the content is less than 2 wt %. When the content is 8 wt % or more, the mechanical strength is not increased. When the content is 15 wt % or more, the melting point for melting a solid material rises, giving rise to the necessity to increase the sintering temperature for the sintering. To avoid this, the Ni content can be, for example, 15 wt % or less, that is, zero wt % or more and less than 15 wt %, particularly, 2 wt % or more and less than 15 wt %, more particularly, 2 wt % or more and less than 8 wt %.

In brief, for example, as to the principal component, Cu can be more than 50 wt % and 93 wt % or less, and Sn can be 5 wt % or more and 15 wt % or less. As to the components of the remainder, CaF₂ can be 2 wt % or more and 6 wt % or less, Pb zero wt % or more and 10 wt % or less, Ni zero wt % or more and less than 15 wt %, and the other remaining components can be zero wt % or more and less than 5 wt %. That is, all the components are added together to amount to 100 wt % in total.

FIG. 2 and FIG. 3 each show a schematic diagram of the surface of the thus-produced copper alloy, that is, the surface of the sintered copper alloy formed as the sliding layer 21. FIG. 4 and FIG. 5 each show a schematic diagram of the cross section of each of FIG. 2 and FIG. 3. FIG. 2 and FIG. 4 each show the copper alloy after the finishing machining process, and FIG. 3 and FIG. 5 each show the copper alloy after the compatibleness (breaking-in) period.

In FIG. 2 to FIG. 5, a dot pattern part designated by reference numeral 22 shows Cu, a blackened part designated by reference numeral 23 shows CaF₂ particles. A whitened (paper color) part designated by reference numeral 24 shows a hole resulting from breaking-away of CaF₂ from the surface of the copper alloy. FIG. 2 to FIG. 5 each show the structure in which CaF₂ particles 23 having an average particle size of 40 μm to 350 μm are uniformly dispersed in a particle form in the matrix of the copper alloy.

The copper alloy after the finishing machining process shown in each of FIG. 2 and FIG. 4 has the surface having undergone the finishing machining process including machining, grinding, lapping and the like after the sintering. The finishing machining process results in the coexistent state of the regions of the holes 24 created after the breaking-away of the CaF₂ particles 23 and the regions of the CaF₂ particles 23 remaining without breaking away. On the other hand, as shown in FIG. 4, the CaF₂ particles 23 in the interior except the surface are dispersed and scattered in the interior without breaking away. Therefore, the strength of the copper alloy does not decrease, and the broken regions (holes 24) of the surface alone function as oil sumps. As a result, the strength of the copper alloy is ensured, while an enhancement in seizure resistance properties is made possible. Since the CaF₂ particles 23 remaining without breaking away from the surface function as a solid lubricant, the effects of enhancing the seizure resistance properties are effective even when the CaF₂ particles 23 remain.

The copper alloy after the compatibleness period shown in each of FIG. 3 and FIG. 5 has experienced the compatibleness (breaking-in) period of about 30 minutes. During this period, the sliding resistance is applied to the surface of the copper alloy, so that the CaF₂ particles 23 further break away from the surface in the condition shown in each of FIG. 2 and FIG. 4 to increase the number of holes 24 serving as the oil sumps. It is seen from this to offer the surface condition with further enhanced seizure resistance properties. In this case, the copper alloy of the sliding layer 21, that is, the copper alloy containing Cu and Sn as the principal components according to the first embodiment has a Mohs hardness of about 4 to 5, and the CaF₂ particles 23 has a Mohs hardness of 4 which is the same degree as the copper alloy. However, since the CaF₂ particles 23 are brittle and easily broken, the CaF₂ particles 23 having broken away during the operating period are discharged without virtually damaging the copper alloy of the sliding layer 21. The sliding opposing part materials are iron-and-steel based materials including cast iron, steel or the like having a Mohs hardness of about 5 to 7, which are harder than the CaF₂ particles 23. Because of this, the CaF₂ particles 23 are discharged without virtually damaging the sliding opposing part materials.

Next, an explanation will be made of a test conducted to confirm the effects of the sliding layer 21 of the sintered copper alloy according to the first embodiment.

Initially, a seizure test was performed using the actual hydraulic motor 1 installing the valve plate 12 with the sliding layer 21 formed of the sintered copper alloy. The sintered copper alloy forming the sliding layer 21 of the valve plate 12 used in the test had Cu and Sn as the principal components, in which Sn was 11 to 13 wt %. The remainder included 3 wt % CaF₂, 1 to 3 wt % Pb, and 4 to 6 wt % Ni as the essential components. The seizure test was performed on each of the three valve plates 12 with the respective average particle sizes of CaF₂ being adjusted to 50 μm, 100 μm and 280 μm. It should be noted that the surface of the cylinder block 8 which was the sliding opposing part of the valve plate 12 was formed of an iron-and-steel based materials (a sliding layer of the sintered copper alloy is not formed).

The seizure test was performed on the hydraulic motor 1 with a higher contact pressure between the sliding surfaces of the valve plate 12 and the cylinder block 8 than usual. Specifically, the motor drive pressure was gradually built up under the condition of constant RPM. Then, the pressure at the time the amount of leakage from the sliding area between the valve plate 12 and the cylinder block 8 sharply increased was evaluated as a seizure limit value. In a concrete manner, a comparison with a valve plate of a sintered copper alloy without CaF₂ produced by the technique according to the aforementioned Patent Document 1 (conventional art) was made.

FIG. 6 shows the test results. In comparison of a seizure limit value with the conventional art, it was confirmed that a seizure limit value than that in the conventional art was obtained in any of the cases of the average particle sizes of CaF₂ of 50 μm, 100 μm, 280 μm.

For the purpose of ascertaining the ranges of percentages by weight and particle sizes of CaF₂ producing a seizure limit value equal to or higher than that in the conventional art from the results of the above-described tests on the actual motor, an element test (seizure limit test) was carried out. In the seizure limit test, after the sliding was performed for 15 minutes in the condition of constant test pressure, the motor was disassembled to check the sliding surface. When any problem did not arise, the test pressure was increased in 0.5 MPa each. Then, the test pressure at the time when the sliding material was transferred to the opposing part material was evaluated as a seizure limit point. Test conditions of the seizure limit test are as follows.

Test Machine: JIS constant-speed friction tester (JIS D4311)

Sliding plate lining: outer diameter Φ 97 mm×inner diameter Φ 54 mm

Area of sliding part: 51 cm²

Opposing part materials: FCD

Sliding speed: 10.8 m/sec

Test pressure: an increase in cylinder pressure of the tester by 0.5 Mpa each from 0.5 MPa (sliding for 15 minutes in each pressure)

Oil temperature: 50° C.

Lubricating oil: Hydraulic operating fluid (VG46)

First, an evaluation test was conducted with the CaF₂ percentage by weight being varied. Two different kinds of copper alloys were prepared as test specimens used in the test. One of the copper alloys had a composition (Cu—Sn—Ni—CaF₂) containing Cu and Sn as principal components, the principal component Sn being 11 to 13 wt %, and the remainder to the principal components including 4 to 6 wt % Ni, and 2 to 3 wt % CaF₂ as essential components.

The other copper alloy had a composition (Cu—Sn—Ni—Pb—CaF₂) containing Cu and Sn as principal components, the principal component Sn being 11 to 13 wt %, and the remainder to the principal components including 1 to 3 wt % Pb, 4 to 6 wt % Ni, and 1 to 6 wt % CaF₂ as essential components. In any alloy (in one copper alloy and in the other copper alloy), the average particle size of CaF₂ was controlled to be 100 μm.

FIG. 7 shows the test results. In the seizure test on the actual motor shown in FIG. 6, the valve plate 12 containing CaF₂ with an average particle size of 100 μm was 1.8 times compared to the conventional art. Because of this, values of the element test data in the same composition and the same average particle size (CaF₂ is 3 wt % and the average particle size is 100 μm) were categorized as equivalent values (1.8 times) in comparison to the conventional art.

In both the Cu—Sn—Ni—Pb—CaF₂ and Cu—Sn—Ni—CaF₂ compositions, it was confirmed that, when CaF₂ was 3 wt % or less, the oil-sump effect on the copper alloy surface described earlier gradually reduced and the seizure limit value also had a tendency to decrease gradually. It was confirmed that in comparison to the conventional art, the Cu—Sn—Ni—CaF₂ composition had a result of a lower seizure threshold value, but, as long as CaF₂ was 2 wt % or more in both the compositions, the seizure limit values were equal to or higher than that in the conventional art.

Next, an evaluation test was conducted with the average particle size of CaF₂ being varied. Two different kinds of copper alloys were prepared as test specimens used in the test. One of the copper alloys had a composition (Cu—Sn—Ni—CaF₂) containing Cu and Sn as principal components, the principal component Sn being 11 to 13 wt %, and the remainder to the principal components including 4 to 6 wt % Ni, and 3 wt % CaF₂ as essential components.

The other copper alloy had a composition (Cu—Sn—Ni—Pb—CaF₂) containing Cu and Sn as principal components, the principal component Sn being 11 to 13 wt %, and the remainder to the principal components including 1 to 3 wt % Pb, 4 to 6 wt % Ni, and 3 wt % CaF₂ as essential components.

FIG. 8 shows the test results. In the seizure test on the actual motor shown in FIG. 6, a ratio of the valve plate 12 containing CaF₂ with an average particle size of 100 μm to the conventional art was 1.8 times. Because of this, values of the element test data in the same composition and the same average particle size (CaF₂ is 3 wt % and the average particle size is 100 μm) were categorized as equivalent values (1.8 times) in comparison to the conventional art. In the case of the Cu—Sn—Ni—Pb—CaF₂ composition, when the average particle size was less than 40 μm and exceeded 350 μm, the seizure limit resulted in a sharp decrease. However, it was confirmed that, in the range of average particle sizes from 40 μm to 350 μm, the seizure limit was equivalent to or higher than that in the conventional art.

In the Cu—Sn—Ni—CaF₂ composition, when the average particle size was 100 μm, the seizure limit was 1.2 times compared to the conventional art. However, estimated from the results of the seizure tests and the element tests using the actual motor on the Cu—Sn—Ni—Pb—CaF₂ composition, it is conceivable that the seizure limit does not sharply decrease in the range of the average particle sizes from 40 to 350 μm. Therefore, it is considered that, in both the Cu—Sn—Ni—Pb—CaF₂ and Cu—Sn—Ni—CaF₂ compositions, a seizure limit value equal to or higher than that in the conventional art can be obtained in the range of the CaF₂ average particle sizes from 40 to 350 μm.

From the above, in a brief account of the results of the seizure test (element tests), it is possible to improve the seizure resistance properties to a level equivalent to or greater than that in the conventional art by controlling the content of CaF₂ to be 2 wt % or more and an average particle size of CaF₂ to fall within a range from 40 to 350 μm.

Next, an element test (erosion test) was conducted also on the amount of cavitation erosion for the purpose of ascertaining the ranges of percentages by weight and particle sizes of CaF₂.

In the erosion test, an ultrasonic erosion test machine was used. A test specimen was attached to a top end of a vibration horn. While a water stream was being sprayed onto the test specimen, ultrasonic waves were emitted to measure changes in weight of the test specimen. In other words, upon emission of ultrasonic waves, cavitation occurred on the surface of the test specimen, leading to occurrence of falling-off of a lining. In this state, the weight of the test specimen was measured in one hour later and in two hours later, and the amount of decrease in weight of the test specimen was calculated, which was then determined as the amount of cavitation erosion. Test conditions in the erosion test are as follows.

Test Machine: Ultrasonic erosion test machine

Test specimen: outer diameter 18 mm×thickness 10 mm (the thickness of lining 1 mm)

Vibration Frequency: 20 kHz

Amplitude: ±37 μm

Water temperature: 50° C.

The test results were evaluated by comparison between the amount of decrease in weight of the test specimen in one hour later and in two hours later and the test results of the copper alloy without CaF₂ produced by the techniques according to Patent Document 1. Ratios to the conventional art referring to a comparison between the amount of wear of the test specimens and the conventional art are plotted along the vertical axis.

First, an evaluation test was conducted with the CaF₂ percentage by weight being varied. Two different kinds of copper alloys were prepared as test specimens used in the test. One of the copper alloys had a composition (Cu—Sn—Ni—CaF₂) containing Cu and Sn as principal components, the principal component Sn being 11 to 13 wt %, and the remainder to the principal components including 4 to 6 wt % Ni, and 2 to 3 wt % CaF₂ as essential components.

The other copper alloy had a composition (Cu—Sn—Ni—Pb—CaF₂) containing Cu and Sn as principal components, the principal component Sn being 11 to 13 wt %, and the remainder to the principal components including 1 to 3 wt % Pb, 4 to 6 wt % Ni, and 1 to 6 wt % CaF₂ as essential components. In any alloy (in one copper alloy and in the other copper alloy), the average particle size of CaF₂ was controlled to be 100 μm.

FIG. 9 shows the test results. In both the Cu—Sn—Ni—Pb—CaF₂ and Cu—Sn—Ni—CaF₂ compositions, there was a tendency that the amount of cavitation erosion was the lower as the amount of CaF₂ was decreased. As a result of the test, a larger amount of cavitation erosion occurred in the use of the Cu—Sn—Ni—Pb—CaF₂ composition. It was confirmed that, as long as CaF₂ was 6 wt % or less, the amount of cavitation erosion was decreased to be lower than that in the conventional art.

Next, an evaluation test was conducted with the average particle size of CaF₂ being varied. Two different kinds of copper alloys were prepared as test specimens used in the test. One of the copper alloys had a composition (Cu—Sn—Ni—CaF₂) containing Cu and Sn as principal components, the principal component Sn being 11 to 13 wt %, and the remainder to the principal components including 4 to 6 wt % Ni, and 3 wt % CaF₂ as essential components.

The other copper alloy had a composition (Cu—Sn—Ni—Pb—CaF₂) containing Cu and Sn as principal components, the principal component Sn being 11 to 13 wt %, and the remainder to the principal components including 1 to 3 wt % Pb, 4 to 6 wt % Ni, and 3 wt % CaF₂ as essential components.

FIG. 10 shows the test results. In the Cu—Sn—Ni—Pb—CaF₂ composition, there was a tendency that the amount of cavitation erosion was decreased to be the lower as the average particle size of CaF₂ was larger. As a result of the test, a larger amount of cavitation erosion occurred in the use of the Cu—Sn—Ni—Pb—CaF₂ composition than in the use of the Cu—Sn—Ni—CaF₂ composition. However, it was confirmed that, as long as the average particle size of CaF₂ was 40 μm or more, the amount of cavitation erosion was decreased to be lower than that in the conventional art.

In a brief account of the results of the erosion test (element tests), it was seen that the amount of cavitation erosion was lower than that in the conventional art and the mechanical strength was ensured in a level equivalent to or greater than that in the conventional art by controlling the CaF₂ content to be 6 wt % or less and a CaF₂ average particle size to be 40 μm or more.

In a brief account of the results of the motor seizure tests and the element tests (seizure limit tests and erosion tests) described above, it was seen that controlling the CaF₂ content to fall within a range of 2 to 6 wt % (2 wt %≦CaF₂ content ratio≦6 wt %) and a CaF₂ average particle size to fall within a range of 40 to 350 μm (40 μm≦CaF₂ average particle size≦350 μm) enabled the compatibility between the seizure resistance properties and the mechanical strength in levels equivalent to or greater than in the conventional art to be achieved.

Particularly, it was confirmed that the compatibility between the seizure resistance properties and the mechanical strength at higher levels was enabled by using Cu and Sn as principal components and using Pb and Ni as well as CaF₂ as essential components for the remainder. In this case, CaF₂ is controlled such that 90 wt % or higher and 100 wt % or less of the total weight of CaF₂ have particle sizes falling within the range from 40 μm to 350 μm. This makes it possible to discriminate the holes 24 caused by failure such as cavities of 500 μm or greater and the like that are regarded as defects in the producing process for the copper alloy, thus offering a copper alloy enabling easy quality control for mass production.

Further, in some techniques in the conventional art, about 10 wt % Pb is contained for an improvement in seizure resistance properties. However, in the first embodiment, since CaF₂ is contained in order to improve the seizure resistance properties, a reduction in the Pb percentage by weight is made possible. In addition, an enhancement in mechanical strength is made possible by containing CaF₂. As a result, in the first embodiment, even when the Pb content is reduced to 3 wt % or less, the seizure resistance properties and the mechanical strength at levels equal to or greater than in the conventional art can be obtained. Accordingly, the first embodiment can also address a recent move to prohibit inclusion or reduce the content of environmental hazardous substances such as Pb contained in various manufactured goods from the viewpoint of environmental conservation.

As described above, according to the first embodiment, the sintered copper alloy formed as the sliding layer 21 on one of the sliding surfaces is a copper alloy containing Cu and Sn as principal components and having a composition including CaF₂ as an essential component for the remainder. In this case, the CaF₂ is controlled to be 2 wt % or more and 6 wt % or less (2 wt %≦CaF₂ content ratio≦6 wt %) and to have an average particle size of 40 μm or more and 350 μm or less (40 μm≦CaF₂ average particle size≦350 μm). As a result, because of the CaF₂ particles 23 scattered in the inside (within the copper alloy), the mechanical strength (the material strength, the cavitation erosion resistance properties) can be ensured. Further, the CaF₂ particles 23 scattered on the surface (sliding surface) break away from the surface to create the holes 24 on the surface, so that the holes 24 function as oil sumps. On the other hand, the CaF₂ particles 23 remaining on the surface function as a solid lubricant between the opposing part surface and the sliding layer 21. As a result, the seizure resistance properties can be ensured.

It should be noted that, when the CaF₂ content is less than 2 wt %, the number of CaF₂ particles 23 scattered on the surface is lower. This causes the deterioration of the function as the oil sumps caused by the breaking-away (hole 24) of the CaF₂ particles 23 and the function as the solid lubricant of the CaF₂ particles 23 remaining on the surface, so that the seizure resistance properties may not be easily ensured. On the other hand, when the CaF₂ content is increased, the oil sumps and the solid lubricant can be increased to cause an improvement in seizure resistance properties. However, when the CaF₂ content exceeds 6 wt %, an increase in the content of CaF₂ with low toughness and an increase in the CaF₂ grain boundaries combine to be likely to reduce the cavitation erosion resistance properties (increase the wear).

Even when the CaF₂ content is 2 to 6 wt %, in the case where, for example, the CaF₂ average particle size is less than 40 μm, the grain boundaries between CaF₂ and metal (copper) increase on the surface of the sliding layer 21, causing the likelihood of a reduction in cavitation erosion resistance properties (increase in wear). On the other hand, when CaF₂ average particle size exceeds 350 μm, for example, the number of holes 24 caused by breaking-away of the CaF₂ particles 23 is decreased, causing the likelihood of a reduction in seizure resistance properties.

By contrast, according to the first embodiment, because CaF₂ is controlled to be 2 to 6 wt % and to have an average particle size of 40 μm to 350 μm, the CaF₂ particles 23 can be distributed in the inside and on the surface of the sliding layer 21 in balance, thus providing the compatibility between ensuring the seizure resistance properties and ensuring the mechanical strength (cavitation erosion resistance properties).

According to the first embodiment, the remainder of the sintered copper alloy formed as the sliding layer 21 has a composition including at least one component or more selected from the group consisting of Pb, Ni, Be, P, Fe, Zn, Al, Si, Mn, Mg, S, Ti, V, Cr, and W, in addition to CaF₂ as the essential component. This makes it possible to provide the compatibility between ensuring the seizure resistance properties and ensuring the mechanical strength at a higher level.

For example, when the composition includes Pb, the amount of Pb component exceeding a solubility limit of the copper alloy is dispersed in the matrix. Because of this, when a state in which seizure occurs during sliding (the surface temperature is higher than the melting point of Pb) takes place, the Pb located around the sliding surface melts and escapes, making it possible to achieve a seizure reduction. As a result, in addition to the effect of improving the seizure resistance properties that is brought about by CaF₂, the seizure reduction effect brought about by Pb can be obtained. Therefore, a synergistic effect of both the effects can bring about a further improvement in seizure resistance properties.

For example, when a composition does not include Pb and includes at least any selected from the group consisting of Ni, Be, P, Fe, Zn, Al, Si, Mn, Mg, S, Ti, V, Cr, and W, the hardness of the copper alloy can be increased, creating an improvement in the mechanical strength. For example, a composition including 11 to 13 wt % (11 wt % or more and 13 wt % or less) Sn in addition to Cu as principal components, and the remainder including 4 to 6 wt % (4 wt % or more and 6 wt % or less) Ni in addition to CaF₂ is made possible.

Further, when a composition includes Pb as well as at least any selected from the group consisting of Ni, Be, P, Fe, Zn, Al, Si, Mn, Mg, S, Ti, V, Cr, and W, the seizure resistance properties and the mechanical strength can both be improved. For example, a composition including 11 to 13 wt % (11 wt % or more and 13 wt % or less) Sn in addition to Cu as principal components, and the remainder including 1 to 3 wt % (1 wt % or more and 3 wt % or less) Pb and 4 to 6 wt % (4 wt % or more and 6 wt % or less) Ni in addition to CaF₂ is made possible.

According to the first embodiment, the remainder of the sintered copper alloy formed as the sliding layer 21 includes CaF₂, Pb and Ni as essential components, and the CaF₂ contained in the sintered copper alloy is controlled such that 90 wt % or higher and 100 wt % less (90 wt %≦content ratio of CaF₂ of predetermined size≦100 wt %) of the total weight of CaF₂ have particle sizes falling within a range of 40 μm or more and 350 μm or less (40 μm≦particle size≦350 μm). This brings about an improvement in quality control for mass production in addition to the compatibility between ensuring the seizure resistance properties and ensuring the mechanical strength at a higher level.

That is, a seizure reduction can be achieved by containing Pb as an essential component, and also an improvement in mechanical strength can be achieved by containing Ni as an essential component. Further, the control of CaF₂ particle size is performed such that 90 wt % or more and 100 wt % or less of the CaF₂ have particle sizes in the range from 40 μm or more to 350 μm or less. This makes it possible to inhibit the hole 24 of a size exceeding 350 μm from being formed on the surface of the sliding layer 21 by the breaking-away of CaF₂. This facilitates discrimination between pin holes and cavities of 500 μm or greater which are regarded as defects of a sintered alloy, and the hole 24 caused by the breaking-away of CaF₂, leading to an improvement in quality control for mass production.

According to the first embodiment, the sliding layer 21 formed of the aforementioned sintered copper alloy is formed on one of the mutually sliding surfaces of the valve plate 12 which is the first member and the cylinder block 8 which is the second member, namely, on the sliding surface 12A of the valve plate 12. Thus, ensuring the seizure resistance properties and ensuring the mechanical strength can be achieved in the sliding area between the valve plate 12 and the cylinder block 8. As a result, as compared with the conventional art, the operation of the hydraulic motor 1 at higher rpm and higher pressure is made possible, leading to downsizing and an increase in output of the hydraulic motor 1. Further, along with the improvement of the seizure resistance properties, an increase in contact pressure in the sliding area is made possible. This makes it possible to reduce the amount of leakage from the sliding area, leading to greater efficiency.

It should be noted that the actual-motor tests of which the results are shown in FIG. 6 were conducted using the hydraulic motor 1 with the sliding layer 21 formed of the sintered copper alloy being formed on one of the sliding surface 12A of the valve plate 12 and the sliding surface 8A of the cylinder block 8, specifically, on the sliding surface 12A of the valve plate 12. Without being limited to the above, however, the sliding layer 21 formed of the sintered copper alloy may be formed on one of the sliding surface 9A of the cylinder 9 and the sliding surface 11B of the piston 11, and on one of the sliding surface 13A of the shoe 13 and the sliding surface 14A of the swash plate 14.

When the sliding layer 21 formed of the aforementioned sintered copper alloy is formed on one of the sliding surface 9A of the cylinder 9 and the sliding surface 11B of the piston 11, ensuring the seizure resistance properties and ensuring the mechanical strength can be achieved in the sliding area between the cylinder 9 and the piston 11. As a result, also from this regard, it is possible to achieve downsizing, an increase in output, and an increase in efficiency of the hydraulic motor 1.

When the sliding layer 21 formed of the aforementioned sintered copper alloy is formed on one of the sliding surface 13A of the shoe 13 and the sliding surface 14A of the swash plate 14, ensuring the seizure resistance properties and ensuring the mechanical strength can be achieved in the sliding area between each shoe 13 and the swash plate 14. As a result, also from this regard, it is possible to achieve downsizing, an increase in output, and an increase in efficiency of the hydraulic motor 1.

Next, FIG. 11 and FIG. 12 show a second embodiment according to the present invention. A feature of the second embodiment is that a sliding layer formed of a sintered copper alloy is formed on a sliding surface of a variable-displacement type and swash-plate type hydraulic rotary machine. Incidentally, in the second embodiment, component elements are identical to those in the above-described first embodiment will be simply denoted by the same reference numerals to avoid repetitions of similar explanations.

In the drawings, indicated at 31 is a casing of the variable-displacement type and swash-plate type hydraulic rotary machine, the casing 31 being formed to be hollow. Specifically, the casing 31 includes a stepped-cylindrical casing body 32 having one end (the right end in FIG. 11 and FIG. 12) formed as a bottom part 32A, and a lid member 33 mounted to the casing body 32 to cover the other end (the left end in FIG. 11 and FIG. 12) of the casing body 32.

The casing body 32 of the casing 31 is provided with an actuator mounting part 32B located apart from the bottom part 32A in the axial direction. The actuator mounting part 32B protrudes outward in the radial direction of the casing body 32. A tilting actuator 37 and the like, described later, are placed inside the actuator mounting part 32B. On the other hand, the lid member 33 of the casing 31 has a pair of supply/discharge passages 33A, 33B formed therein.

The casing 31 has a first oil supply port 31A formed to continuously extend in the lid member 33 and the casing body 32. The first oil supply port 31A is connected to the supply/discharge passages 33A of the lid member 33 to permit the flow of hydraulic oil (operating oil) in the supply/discharge passage 33A. The first oil supply port 31A is provided for a supply of the hydraulic oil in the supply/discharge passage 33A as lubricating oil via a second oil supply port 35B formed in a later-described swash plate support member 35 to a sliding area between the swash plate support member 35 and a swash plate 34.

The swash plate 34 is tiltably mounted in the casing 31. The swash plate 34 is mounted via the later-described swash plate support member 35 on the bottom part 32A of the casing body 32. Here, the swash plate 34 includes a swash plate body 34A, and a smooth plate 34C fixed to a front side of the swash plate body 34A and having a sliding surface 34B formed thereon. The swash plate 34 is structured to allow each shoe 13 to slide on one end face (the left end face in FIG. 11 and FIG. 12) facing the cylinder block 8, specifically, on the sliding face 34B of the smooth plate 34C.

The swash plate 34 forms a displacement varying unit, in which a convex-curved sliding surface 34D is formed on the other end face (the right end face in FIG. 11 and FIG. 12) which is the backside of the swash plate 34 (the swash plate body 34A). The sliding surface 34D is structured to tiltably slide on each tilting slide surface 35A of the swash plate support member 35. The swash plate 34 is tiltably driven to tilt about a swash-plate supporting point by the later-described tilting actuator 37.

The swash plate support member 35 is mounted on the bottom part 32A of the casing body 32. The swash plate support member 35 is placed around the rotational shaft 5 on the backside of the swash plate 34, and fixed to the bottom part 32A of the casing body 32. The swash plate support member 35 has a pair of the tilting slide surfaces 35A formed as a concave-curved sliding surface for tiltable support of the swash plate 34, the tilting slide surfaces 35A sliding on the sliding surface 34D of the swash plate 34. The tilting slide surfaces 35A are located respectively on the left, right (or above, below) sides of the rotational shaft 5.

The swash plate support member 35 has the second oil supply port 35B formed to be connected to the first oil supply port 31A of the casing 31. The second oil supply port 35B is provided for passage of the hydraulic oil flowing from the first oil supply port 31A. One end (the left end in FIG. 11) of the second oil supply port 35B opens on the tilting slide surface 35A. Thus, a portion of the hydraulic oil supplied from the cylinder port 10 and then flowing through the supply/discharge passage 33A of the lid member 33 is supplied via the first oil supply port 31A and the second oil supply port 35B into the sliding area between the swash plate 34 and the swash plate support member 35, specifically, into between the sliding surface 34D of the swash plate 34 and the tilting slide surface 35A of the swash plate support member 35.

A tilting lever 36 is formed integrally with a side part of the swash plate 34. The tilting actuator 37 is placed in the actuator mounting part 32B of the casing body 32. The tilting actuator 37 tiltably drives the swash plate 34 together with the tilting lever 36 upon supply/discharge of tilting-control pressure from a regulator, not shown.

In the second embodiment, during the operation, the cylinder 9 and the piston 11 in the cylinder block 8 slide on each other, the valve plate 12 and the cylinder block 8 slide on each other, and the shoe 13 and the swash plate 14 slide on each other. In addition, with the tilting driving of the swash plate 34, the swash plate 34 as the “second member” slides to be displaced with respect to the swash plate support member 35 as the “first member”. In this case, the swash plate support member 35 has the tilting slide surface 35A as the “first sliding surface” while the swash plate 34 has the sliding surface 34D as the “second sliding surface”. The second oil supply port 35B as the “oil passage” opens on the tilting slide surface 35A of the swash plate support member 35.

In the case of the second embodiment, at least one set of “the first sliding surface and the second sliding surface” of the four sets of “the first sliding surfaces and the second sliding surfaces” is, for example, “the tilting slide surface 35A of the swash plate support member 35 and the sliding surface 34D of the swash plate 34”. In this case, the sliding layer 21 as similar to the case of the aforementioned first embodiment is formed on one of the sliding surfaces composed of the tilting slide surface 35A of the swash plate support member 35 and the sliding surface 34D of the swash plate 34.

In the second embodiment, the sliding layer 21 is formed on one of the tilting slide surface 35A of the swash plate support member 35 and the sliding surface 34D of the swash plate 34 as described above. The basic function is not particularly different from that in the aforementioned first embodiment.

In particular, in the case of the second embodiment, ensuring the seizure resistance properties and ensuring the mechanical strength can be achieved in the sliding area between the swash plate support member 35 and the swash plate 34. As a result, as similar to the case of the aforementioned first embodiment, it is possible to achieve downsizing, an increase in output, and an increase in efficiency of the hydraulic rotary machine.

Next, FIG. 13 shows a third embodiment according to the present invention. A feature of the third embodiment is that a sliding layer formed of a sintered copper alloy is formed on a sliding surface of a variable-displacement type and bent-axis type hydraulic rotary machine. It should be noted that, in the third embodiment, the component elements that are identical to those in the foregoing first embodiment will be simply denoted by the same reference numerals to avoid repetitions of similar explanations.

In the drawings, indicated at 41 is a casing of the variable-displacement type and bent-axis type hydraulic rotary machine, the casing 41 being formed in approximately a hollow cylindrical shape. A head cover 51 to be described later is fixedly attached to a head end face (the left end face in FIG. 13) of the casing 41 to cover the opening of the casing 41.

A rotational shaft 42 is rotatably fitted through a pair of bearings 43 in the casing 41. A drive disk 42A is provided integrally with the top end of the rotational shaft 42.

A cylinder block 44 is provided in the casing 41. The cylinder block 44 rotates together with the rotational shaft 42 through a piston 49 to be described later. Here, the cylinder block 44 has a center shaft insertion hole 44A bored along the center axis. The cylinder block 44 has an end face facing a valve plate 50 to be described later and formed as a concave-spherical sliding surface (switching sliding surface) 44B. In the cylinder block 44, a cylinder 45 to be described later is formed in conjunction with a cylinder port 46.

A plurality of cylinders 45 are independently formed (bored) in the cylinder block 44. The cylinders 45 are respectively spaced at regular intervals in the circumferential direction of the cylinder block 44, and each extend in the axial direction of the cylinder block 44. One end (the right end in FIG. 13) of each of the cylinders 45 opens on an end face of the cylinder block 44. In the other end (the left end in FIG. 13) of each cylinder 45, the cylinder port 46 is formed. The inner surface of each cylinder 45 is formed as a sliding surface 45A on which a sliding surface 49B of a piston 49 to be described later slides. The cylinder port 46 is formed (bored) in a position corresponding to each cylinder 45 to open on a sliding surface 44B of the cylinder block 44. The cylinder port 46 communicates intermittently with supply and discharge ports 50D, 50E of the valve plate 50 to be described later.

A center shaft 47 is inserted through the center shaft insertion hole 44A for centering of the cylinder block 44. One end (the right end in FIG. 13) of the center shaft 47 is connected via a spherical part 47A to the drive disk 42A to be capable of being pivoted around. The other end of the center shaft 47 is inserted into a center hole 50A of the valve plate 50 described later. A spring 48 is located inside the cylinder block 44 to be provided with tension between the cylinder block 44 and the center shaft 47. The spring 48 provides the cylinder block 44 with an initial load toward the valve plate 50.

A plurality of the pistons 49 are inserted individually into the respective cylinders 45 of the cylinder block 44 to be capable of reciprocating therein. A spherical part 49A is provided at a projecting end which is one end of each of the pistons 49. The spherical part 49A is supported by (connected to) the drive disk 42A to be capable of tilting therein. The outer peripheral surface of each piston 49 is formed as a sliding surface 49B sliding on the sliding surface 45A which is the inner surface of the corresponding cylinder 45.

The valve plate 50 is placed between the cylinder block 44 and the head cover 51 to be described later. The valve plate 50 has the center hole 50A formed in a central position. The valve plate 50 has one end face (the right end face in FIG. 13) facing the cylinder block 44 and formed as a convex-arc-shaped sliding surface 50B on which the sliding surface 44B of the cylinder block 44 slides. A convex-curved sliding surface 50C is formed on the other end face of the valve plate 50. The sliding surface 50C tiltably slides on a tilting slide surface 51A of the head cover 51. The valve plate 50, together with the cylinder block 44, is tiltably driven to tilt about a valve-plate supporting point by a tilting actuator 52 to be described later.

A pair of the supply and discharge ports 50D, 50E are formed in the valve plate 50 such that piston top dead center and piston bottom dead center are located between the supply and discharge ports 50D, 50E. The supply and discharge ports 50D, 50E are provided for passage of the hydraulic oil (operating oil) flowing between the cylinder 45 and the supply/discharge passages (not shown) formed in the head cover 51. One ends (the right ends in FIG. 13) of the supply and discharge ports 50D, 50E open on the sliding surface 50B to communicate with the cylinders 45 through the cylinder ports 46. The other ends (the left ends in FIG. 13) of the supply and discharge ports 50D, 50E open on the sliding surface 50C to communicate with the respective supply/discharge passages of the head cover 51.

The head cover 51 is provided on the head end face of the casing 41 to serve as a valve plate support member. In the head cover 51, the concave-curved tilting slide surface 51A sliding with the sliding surface 50C of the valve plate 50 is formed at one end facing the valve plate 50. The head cover 51 is provided with the tilting actuator 52 tiltably driving the cylinder block 44 together with the valve plate 50.

In the case of the third embodiment, during operation, the cylinder 45 of the cylinder block 44 serving as “a first member” and the piston 49 serving as “a second member” slide with each other. The valve plate 50 serving as “a first member” and the cylinder block 44 serving as “a second member” slide with each other. In addition, with the tilting driving of the valve plate 50 together with the cylinder block 44, the valve plate 50 as a “first member” slides to be displaced with respect to the head cover 51 as a “second member”.

In this case, the cylinder block 44 has the sliding surface 45A of the cylinder 45 serving as “the first sliding surface”, while the piston 49 has the sliding surface 49B serving as “the second sliding surface”, in which the cylinder port 46 serving as “an oil passage” opens on the sliding surface 45A of the cylinder 45. The valve plate 50 has the sliding surface 50B serving as “the first sliding surface”, while the cylinder block 44 has the sliding surface 44B serving as “the second sliding surface”, in which the supply and discharge ports 50D, 50E serving as “oil passages” open on the sliding surface 50B of the valve plate 50, and the cylinder port 46 serving as “an oil passage” opens on the sliding surface 44B of the cylinder block 44. The valve plate 50 has the sliding surface 50C serving as “the first sliding surface”, while the head cover 51 has the tilting sliding surface 51A serving as “the second sliding surface”, in which the supply and discharge ports 50D, 50E serving as “oil passages” open on the sliding surface 50C of the valve plate 50.

In the case of the third embodiment, at least one set of “the first sliding surface and the second sliding surface” of the three sets of “the first sliding surfaces and the second sliding surfaces” is, for example, “the sliding surface 50C of the valve plate 50 and the tilting slide surface 51A of the head cover 51”. In this case, the sliding layer 21 as similar to the case of the aforementioned first embodiment is formed on one of the sliding surfaces composed of the sliding surface 50C of the valve plate 50 and the tilting slide surface 51A of the head cover 51.

In the third embodiment, the sliding layer 21 is formed on one of the sliding surface 50C of the valve plate 50 and the tilting slide surface 51A of the head cover 51 as described above. The basic function is not particularly different from that in the aforementioned first embodiment.

In particular, in the case of the third embodiment, ensuring the seizure resistance properties and ensuring the mechanical strength can be achieved in the sliding area between the valve plate 50 and the head cover 51. As similar to the case of the aforementioned first embodiment, this makes it possible to achieve downsizing, an increase in output, and an increase in efficiency of the hydraulic rotary machine.

It should be noted that in the aforementioned first embodiment the explanation has been made by taking the case of using the hydraulic rotary machine as the hydraulic motor 1 as an example. However, the present invention is not limited to this. For example, the hydraulic rotary machine may be used as a hydraulic pump. As regards the hydraulic oil, liquids such as various oils, water, liquid chemicals and the like in addition to the operating oil can be used as hydraulic oils. The above points are true for the other embodiments.

The above-described third embodiment has been described by taking the variable displacement type hydraulic rotary machine as an example of the bent-axis type hydraulic rotary machine. However, the present invention is not limited to this. For example, the present invention may be applied to a fixed-displacement type and bent-axis type hydraulic rotary machine.

The above-described first to third embodiments have been described by taking the axial-piston type hydraulic rotary machine as an example of the hydraulic rotary machine. However, the present invention is not limited to this. For example, the present invention may be applied to a radial-piston type hydraulic rotary machine. In the case of the swash-plate type hydraulic rotary machine, the shoe of the piston and the swash plate slide with each other (a member on which the shoe slides is the swash plate). On the other hand, in the case of the radial-piston type hydraulic rotary machine, for example, a shoe and a cam ring slide with each other (a member on which the shoe slides is the cam ring). In this case, the sliding layer formed of the aforementioned sintered copper alloy can be formed on one of sliding surfaces of the shoe and the cam ring.

In addition, the hydraulic rotary machine can be used not only as a hydraulic pump, a hydraulic motor and the like installed in construction machines, such as hydraulic excavators, hydraulic cranes, wheel loaders and the like, but also as a hydraulic pump, a hydraulic motor and the like installed in various kinds of industrial machinery.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1: Hydraulic motor (Hydraulic rotary machine)     -   2, 31, 41: Casing     -   5, 42: Rotational shaft     -   8, 44: Cylinder block (First member, Second member)     -   8A, 44B: Sliding surface (Second sliding surface)     -   9, 45: Cylinder     -   9A, 45A: Sliding surface (First sliding surface)     -   10, 46: Cylinder port (Oil passage)     -   11, 49: Piston (Second member)     -   11B, 49B: Sliding surface (Second sliding surface)     -   11C: First oil supply port     -   12, 50: Valve plate (First member)     -   12A, 50B, 50C: Sliding surface (First sliding surface)     -   12B, 12C, 50D, 50E: Supply and discharge port (Oil passage)     -   13: Shoe (First member)     -   13A: Sliding surface (First sliding surface)     -   13B: Second oil supply port (Oil passage)     -   14, 34: Swash plate (Second member)     -   14A, 34B, 34D: Sliding surface (Second sliding surface)     -   21: Sliding layer     -   35: Swash plate support member (First member)     -   35A: Tilting slide surface (First sliding surface)     -   35B: Second oil supply port (Oil passage)     -   51: Head cover (Second member)     -   51A: Tilting slide surface (Second sliding surface) 

1. A hydraulic rotary machine, comprising: first members (8, 12, 13, 35, 44, 50) that include first sliding surfaces (9A, 12A, 13A, 35A, 45A, 50B, 50C); and second members (8, 11, 14, 34, 44, 49, 51) that include second sliding surfaces (8A, 11B, 14A, 34B, 34D, 44B, 49B, 51A) sliding with respect to said first sliding surfaces (9A, 12A, 13A, 35A, 45A, 50B, 50C), wherein one ends of oil passages (10, 11C, 12B, 12C, 13B, 35B, 46, 50D, 50E), through which an hydraulic oil flows, open on at least any of said first sliding surfaces (9A, 12A, 13A, 35A, 45A, 50B, 50C) and said second sliding surfaces (8A, 11B, 14A, 34B, 34D, 44B, 49B, 51A), characterized in that: a sliding layer (21) formed of a sintered copper alloy is formed on one of said first sliding surfaces (9A, 12A, 13A, 35A, 45A, 50B, 50C) and said second sliding surfaces (8A, 11B, 14A, 34B, 34D, 44B, 49B, 51A); said sliding layer (21) has a composition including Cu and Sn as principal components and the remainder as remaining components; said remainder includes 2 wt % to 6 wt % CaF₂ as an essential component, and an average particle size of said CaF₂ is controlled to fall within a range from 40 μm to 350 μm; and the other sliding surface of said first sliding surface (9A, 12A, 13A, 35A, 45A, 50B, 50C) and said second sliding surface (8A, 11B, 14A, 34B, 34D, 44B, 49B, 51A) is formed of a sliding layer of iron-and-steel materials.
 2. The hydraulic rotary machine according to claim 1, wherein said remainder of said sliding layer (21) has a composition including at least one component or more selected from the group consisting of Pb, Ni, Be, P, Fe, Zn, Al, Si, Mn, Mg, S, Ti, V, Cr and W, in addition to said CaF₂ as the essential component.
 3. The hydraulic rotary machine according to claim 2, wherein a composition of said principal components of said sliding layer (21) includes 11 wt % to 13 wt % of said Sn in addition to said Cu; and a composition of said remainder of said sliding layer (21) includes 4 wt % to 6 wt % of said Ni in addition to said CaF₂.
 4. The hydraulic rotary machine according to claim 2, wherein a composition of said principal components of said sliding layer (21) includes 11 wt % to 13 wt % of said Sn in addition to said Cu; and a composition of said remainder of said sliding layer (21) includes 1 wt % to 3 wt % of said Pb and 4 wt % to 6 wt % of said Ni in addition to said CaF₂.
 5. The hydraulic rotary machine according to claim 1, wherein said remainder of said sliding layer (21) includes Pb and Ni as essential components in addition to said CaF₂ as the essential component, and said CaF₂ is controlled to include 90 wt % to 100 wt % of said CaF₂ having particle sizes falling within the range from 40 μm to 350 μm.
 6. The hydraulic rotary machine according to claim 1, comprising: a hollow casing (2, 31, 41); a rotational shaft (5, 42) that is rotatably mounted inside said casing (2, 31, 41); a cylinder block (8, 44) that is placed inside said casing (2, 31, 41) to rotate together with said rotational shaft (5, 42), said cylinder block (8, 44) being provided with a plurality of cylinders (9, 45) formed therein to be spaced in a circumferential direction and extend in an axial direction, and cylinder ports (10, 46) formed to open on an end face in positions corresponding to said respective cylinders (9, 45); a plurality of pistons (11, 49) that are inserted into said respective cylinders (9, 45) of said cylinder block (8, 44) to be capable of reciprocating therein; and a valve plate (12, 50) that is placed between said casing (2, 31, 41) and said cylinder block (8, 44) and includes supply and discharge ports (12B, 12C, 50D, 50E) formed to communicate with said respective cylinders (9, 45) through said cylinder ports (10, 46), wherein said first member comprises said valve plate (12, 50) including said supply and discharge ports (12B, 12C, 50D, 50E) formed to be said oil passages; and said second member comprises said cylinder block (8, 44) sliding on said valve plate (12, 50) and including said cylinder ports (10, 46) formed to be said oil passages.
 7. The hydraulic rotary machine according to claim 1, comprising: a hollow casing (2, 31); a rotational shaft (5) that is rotatably mounted inside said casing (2, 31); a cylinder block (8) that is placed inside said casing (2, 31) to rotate together with said rotational shaft (5), said cylinder block (8) being provided with a plurality of cylinders (9) formed therein to be spaced in a circumferential direction and extend in an axial direction, and cylinder ports (10) formed to open on an end face in positions corresponding to said respective cylinders (9); a plurality of pistons (11) that are inserted into said respective cylinders (9) of said cylinder block (8) to be capable of reciprocating therein and include first oil supply ports (11C) formed therein; a valve plate (12) that is placed between said casing (2, 31) and said cylinder block (8) and includes supply and discharge ports (12B, 12C) formed to communicate with said respective cylinders (9) through said cylinder ports (10); a plurality of shoes (13) that are mounted to projecting ends of said respective pistons (11) to be capable of tilting around and include second oil supply ports (13B) formed therein to be connected to said first oil supply ports (11C); and a swash plate (14, 34) that is placed on the opposite side of said cylinder block (8) from said valve plate (12) and on which said respective shoes (13) slide, wherein said first member comprises each of said shoes (13) including said second oil supply port (13B) formed to be said oil passage; and said second member comprises said swash plate (12) on which each of said shoes (13) slides.
 8. The hydraulic rotary machine according to claim 1, comprising: a hollow casing (2, 31, 41); a rotational shaft (5, 42) that is rotatably mounted inside said casing (2, 31, 41); a cylinder block (8, 44) that is placed inside said casing (2, 31, 41) to rotate together with said rotational shaft (5, 42), said cylinder block (8, 44) being provided with a plurality of cylinders (9, 45) formed therein to be spaced in a circumferential direction, and cylinder ports (10, 46) formed to open on an end face in positions corresponding to said respective cylinders (9, 45); and a plurality of pistons (11, 49) that are inserted into said respective cylinders (9, 45) of said cylinder block (8, 44) to be capable of reciprocating therein, wherein said first member comprises said cylinder block (8, 44) including said cylinder ports (10, 46) formed to be said oil passages; and said second member comprises said pistons (11, 49) sliding with respect to said cylinders (9, 45) of said cylinder block (8, 44).
 9. The hydraulic rotary machine according to claim 1, comprising: a hollow casing (31); a rotational shaft (5) that is rotatably mounted inside said casing (31); a cylinder block (8) that is placed inside said casing (31) to rotate together with said rotational shaft (5), said cylinder block (8) being provided with a plurality of cylinders (9) formed therein to be spaced in a circumferential direction and extend in an axial direction, and cylinder ports (10) formed to open on an end face in positions corresponding to said respective cylinders (9); a plurality of pistons (11) that are inserted into said respective cylinders (9) of said cylinder block (8) to be capable of reciprocating therein; a valve plate (12) that is placed between said casing (31) and said cylinder block (8) and includes supply and discharge ports (12B, 12C) formed to communicate with said respective cylinders (9) through said cylinder ports (10); a plurality of shoes (13) that are mounted to projecting ends of said respective pistons (11) to be capable of tilting around; a swash plate (34) that includes one end face facing said cylinder block (8) to allow each of said shoes (13) to slide thereon and the other end face on which a convex-curved sliding surface (34D) is formed, and is tiltably mounted to tilt about a swash-plate supporting point; and a swash plate support member (35) that includes a concave-curved tilting slide surface (35A) formed to allow said sliding surface (34D) of said swash plate (34) to slide thereon, and an oil supply port (35B) formed therein for passage of the hydraulic oil supplied from said cylinder ports (10), wherein said first member comprises said swash plate support member (35) including said oil supply port (35B) formed therein to be said oil passage; and said second member comprises said swash plate (34) sliding with respect to said swash plate support member (35).
 10. The hydraulic rotary machine according to claim 1, comprising: a hollow casing (41); a rotational shaft (42) that is rotatably mounted inside said casing (41) and includes a drive disk (42A) at a top end; a cylinder block (44) that is placed inside said casing (41) to rotate together with said rotational shaft (42), said cylinder block (44) being provided with a plurality of cylinders (45) formed therein to be spaced in a circumferential direction and extend in an axial direction, and cylinder ports (46) formed to open on an end face in positions corresponding to said respective cylinders (45); a plurality of pistons (49) that are inserted into said respective cylinders (45) of said cylinder block (44) to be capable of reciprocating therein, and include projecting ends supported by said drive disk (42A) of said rotational shaft (42) to be capable of tilting therein; a valve plate (50) that includes one end face facing said cylinder block (44) to allow said cylinder block (44) to slide thereon and the other end face on which a convex-curved sliding surface (50B) is formed, and is tiltably mounted to tilt together with said cylinder block (44) about a valve-plate supporting point; and a head cover (51) that includes a concave-curved tilting slide surface (51A) to allow said sliding surface (50C) of said valve plate (50) to slide on, wherein said first member comprises said valve plate (50) including supply and discharge ports (50D) formed to be said oil passages communicating with said respective cylinders (45) through said cylinder ports (46); and said second member comprises said head cover (51) on which said valve plate (50) slides. 